chore: Update DevEnv to v2.0.6

[tguzik]

This PR:

• Updates DevEnv to the latest release - v2.0.6:
  • Release notes: https://github.com/cachix/devenv/releases/tag/v2.0.6
  • In CI this version will be installed using the full commit SHA instead of a tag name - will bring that step of the CI pipeline up to parity with pinned actions enforced by zizmor.
• Updates the Release Changelog workflow to create the release entry using GH CLI instead of a third party action.
• Updates Maven config to validate SCM links right before the release.